The present invention relates to foam generating nozzles which, while having application for the dispensing of a wide variety of chemicals, has its most important application in the dispensing of cleaning chemicals.
The application of chemicals in a foamed condition is frequently desirable for a number of reasons. Thus, it permits the application of chemicals with lower spray rates and active chemical content with the advantage of reduced costs. Also, especially when spraying vertical or downwardly facing horizontal surfaces, maximum contact time of the foamed material on the surface involved is achieved. Additionally, it eliminates the health and safety hazards caused frequently by liquid sprays which by splashing or otherwise forms tiny droplets or a fine mist which is inhaled and strikes the eyes to cause great discomfort and sometimes serious harm to the persons involved. The application of the material in a foamed state reduces or eliminates the tiny droplets or mist formation which causes these health and safety hazards.
The application of agricultural chemicals by spraying from airplanes and the like by foam generating equipment including a nozzle unit which mixes air with the liquid chemical is well known. Occasionally, cleaning chemicals have been applied by foam-producing aerosol and other type dispensing units. Also, the foaming of a mixture of water and a foaming agent issuing from a nozzle is in common use by firemen.
Many materials such as soaps can be readily foamed by mild agitation, and other materials are more difficult to apply in the foamed condition. Foaming agents can sometimes be added to the latter materials to increase their foamability when agitated by passage through an aerosol nozzle or when mixed with air in an aerating nozzle.
The type of foam spray obtained by a particular foam generating nozzle unit is a function of a number of factors, such as the nature of the material being sprayed, the pressure of the material when applied to the nozzle unit and the design of the nozzle unit. Also, the desired consistency of the foam to be developed by a particular nozzle unit depends upon the particular application involved. Usually, for applications involving a prolonged desired retention on vertical and downwardly facing horizontal surfaces, it is desirable to apply the material involved as a thick foam. Thick foams usually comprises small bubbles which have a maximum penetrating power for porous surfaces. In some applications, the throw of the stream produced by the nozzle is important to make it convenient to cover large areas with the foam product quickly and easily. With some foam generating nozzle units having an adjustment of foam thickness, the desired thickest foam is achieved at a serious sacrifice of stream throw, and so a compromise must be made involving both foam thickness and stream throw considerations. It is advantageous, therefore, that a given foam generating nozzle unit be adjustable to provide the desired degree of foaming action, preferably without much sacrifice of stream throw.
One foam generating sprayer heretofore developed and over which the present invention is an improvement is the spray assembly disclosed in U.S. Pat. No. 3,918,647, granted Nov. 11, 1975. The foam sprayer disclosed therein provides a progressive control over the degree and quality of foaming action achieved with a unique foam generating nozzle unit of the air aspirating type by varying the angle of divergence of a liquid stream issuing from an orifice directed into a pressure-reducing passageway including most advantageously a sharply outwardly tapered portion terminating in a restricted throat passageway portion opening into an expansion chamber. The narrowest useful stream flowing from the orifice is a relatively concentrated liquid stream which initially strikes the walls of the throat passageway portion to produce a stream with a long throw but with a modest degree of foam. By progressively increasing the angle of the stream flowing from the orifice, the stream becomes less concentrated and progressively more mist-like and strikes greater extents of the pressure-reducing passageway including said tapered portion thereof. An unexpectedly sudden increase in foaming action occurs with only an insignificantly modest reduction in the spray throw when the widest portion of the diverging stream issuing from the orifice strikes the end section of the tapered portion of the pressure-reducing passageway. Such a spray pattern was found generally to produce foam with good throw. However, even thicker foams were achieved when the widest portion of the diverging stream initially strikes the pressure-reducing passageway at points substantially behind the end section of the tapered passageway portion but the progressively thicker foams are achieved with progressively reduced throws which reach impractical magnitudes after only a small adjustment.
Many prior art non-foaming sprayers provide for the progressive variation of the angle of divergence of a liquid stream emanating from an orifice by the rotation of a member forming the orifice. The rotatable member is usually threaded over the head of the sprayer and the spray angle is varied as the orifice is variably spaced from another orifice within the sprayer head. It usually takes only a small fraction of a revolution of the rotatable orifice-forming member to vary the spray pattern from the narrowest to the widest angle of divergence involved. The use of such an adjusting means in a foam producing sprayer of the kind just described makes the adjustment for an optimum foam quality a burdensome and sometimes difficult operation.
It is, accordingly, an object of the present invention to provide an improvement in the foam generating spray apparatus disclosed in said U.S. Pat. No. 3,918,647, which provides a less sensitive more easily adjusted control for varying the foam quality in foam producing sprayers.
Another object of the present invention is to provide a spray generating nozzle unit which provides for an easily controlled variation in the areas of a foam producing passageway struck by a stream issuing from an orifice, to enable the user readily to achieve an optimum desired degree of foaming with substantial throw distances, where desired.